FR2989832A1 - SOURCE OF CURRENT POLARIZED IN SPINS - Google Patents

Abstract

Device for filtering 75% or more of 75%, preferably more than 85%, of an electron flow, passing through the device at a temperature above -220 ° C, depending on the state of polarization of said electrons , comprising: - an electrically conductive material, called substrate (10), whose first face (11) has magnetic properties; an organic layer (20) comprising a first face (21) opposite a second face (22), the first face (21) comprising at least partly a set of atoms substantially in the same plane, and linked together by atomic links parallel or substantially parallel to the first face (11) of the substrate (10), and in contact with the first face (11) so as to form an interface, said filtering interface.

Description

TECHNICAL FIELD This application relates to the technical field of electronics, specifically that of spintronics. The invention particularly relates to a device for filtering the electrons passing through it, depending on the orientation of their spin, as well as a filtering method. STATE OF THE PRIOR ART Technological advances in the semiconductor industry have greatly reduced the dimensions of electronic devices, thus increasing their power and complexity. Today, the realization of these devices at the atomic scale faces new difficulties, particularly related to the physical phenomena occurring on this scale. To continue to increase the performance of semiconductors, it is therefore necessary to develop devices based on new concepts. One of these concepts is to exploit the quantum property of the spin of electrons, in order to store information. This is the technical field of spintronics. Electrons are characterized by several intrinsic values, in particular by their kinetic moment or "spin" in English. Because of the uncertainty principle of atomic scale measurements, the measurement of the spin of an electron is possible only according to a single observable or direction, and its value can be positive or negative. These states are named respectively "spin up" and "spin down". To exploit this characteristic at the industrial level, it is necessary to develop devices capable of selecting and / or reading the state of polarization of the electron spins. The devices for selecting or filtering electrons according to the orientation of their spin, are called spin injector devices. It is sought that they satisfy several of the criteria below to be industrially exploitable: 1) allow to select or filter more than 80% of the electrons passing through the device, depending on the polarization state of their spin; 2) and / or preserve this filtration rate at operating temperatures at least equal to or higher than the temperature of the liquid nitrogen, of the order of -200 ° C, or preferably at operating temperatures of microelectronic devices that is, in a temperature range of -20 ° C to 300 ° C; 3) and / or be simple and economical to achieve; 4) and / or be of nanometric dimensions; 5) and / or to allow the filtered electrons to be injected, according to the orientation of their spin, into environments favorable to their propagation, without modifying the state of polarization of said spins. Currently, several spin injector devices are under development.

Some spin injectors exploit the tunnel effect to filter electrons. This effect is observed when a barrier, called tunnel barrier, is interposed between two conductive elements. Physically, the tunnel barrier is a medium that is not conducive to the diffusion of electrons. This medium can be insulating or semiconductor. Quantum properties, such as the spin orientation of a particle, moving between two conductors tunnel effect, are preserved during this transport. It is then possible to use this property to convey information between two ferromagnetic conductive elements. The state of polarization of the electrons, making it possible to encode information thanks to the orientation of the magnetization of a ferromagnetic conductive element, can then be detected by modulating the relative orientation of the magnetization of a second conductor ferromagnetic placed on the other side of the tunnel barrier, the assembly forming a magnetic tunnel junction. By placing the device in a state of parallel or antiparallel magnetization of the two ferromagnetic layers, it is thus possible to measure the degree of spin polarization of the current flowing through the device. Since the current flows from one electrode towards the other, the functions of polarization in current spin and of detection or reading of this polarization, are attributed to each of the two interfaces of the magnetic tunnel junction, according to the sign. of the current. It is then possible to reverse the polarization and spin detection assignment of the current at the interfaces simply by changing the sign of the current flowing through the device [Fert, Nobel Lectures 2008]. The spin polarization capabilities of a magnetic tunnel junction can be increased tenfold by selecting a tunnel barrier of electronic structure appropriate to that of the adjacent ferromagnetic electrodes. In this case, certain highly spin polarized conduction electron wave functions within the ferromagnetic layer will pass through the barrier more easily, resulting in a strongly spin-polarized current (Bowen et al., Physical Review B). 73, R140408 (2006)). This effect has been observed, for example, by interposing a layer of magnesium oxide between two layers of iron alloy (Appl Phys Lett 90, 212507 (2007)). Measurements at room temperature then revealed that 85% of the electrons crossing the interfaces of this type of device have their spin polarized in the same direction and the same direction. Unfortunately, this electron filtering mechanism generates a consequent increase in the electrical resistance of the device. At the submicron scale, the device has a resistance value too large to favorably consider its use in the microelectronics industry. This type of device does not check the fourth criterion above. In order to reduce the resistance value, the tunnel barrier may be substituted by half-metallic materials which have the particularity of being metallic for polarized spin electrons in a given direction and direction, and of being insulating for electrons having their spin polarized in the same direction and a reverse direction. This type of device 10 makes it possible to filter in spins of electrons of the order of 95% to 99%. Unfortunately, these measurements could be obtained only at temperatures of the order of -260 ° C. (J. Phys .: Condens Matter 19, 315208 (2007)). In addition, these devices are difficult to perform because of the complex composition and structure of the half-metal layers. Another development path is the use of an organic layer as a tunnel barrier. The organic materials, because of their low mass compared to that of the inorganic materials, offer the advantage of weakly interacting with the polarization state of the conduction electrons. Thus, their spins are much less disturbed when they pass through this type of material on mesoscopic thicknesses (10-1000 nm). However, it is necessary to successfully inject spin-polarized charge carriers within these materials. Therefore, recent research efforts have focused on the spin polarization of organic materials at the interface with a ferromagnetic metal layer. Recent work has shown, by means of a semi-metallic ferromagnetic alloy (J. Phys: Condens Matter 19, 315208 (2007)), the high potential of this type of interface as a spin injector device. Again, the most convincing results were obtained only for temperatures below -170 ° C (Nature Physics 6, 615 (2010)). A major disadvantage of this type of device is the loss of its filtering qualities when the temperature increases. The filtering mechanisms involved are currently misunderstood. It is considered by the scientific community that this loss of filtering is due to extrinsic phenomena, amplified when the temperature of the device increases (Nature Physics 6, 562 (2010)). Operation in an industrial electronic environment is therefore not viable. Theoretical work (Javaid et al, Physical Review Letters 105, 077201 (2010)) predicted at zero temperature (T = -273.15 ° C) that the interface between a ferromagnetic layer of Co and a molecular plane of phthalocyanines of Manganese could be spin-polarized, but this polarization, even by removing the central manganese site (referred to as H2Pc), would not have a sufficient yield, less than 60%, to be used industrially in a competitive manner. The same observation can be made from other theoretical and experimental results on the properties of Fe, Co or Cu phthalocyanine interfaces with ferromagnetic Co metals or Fe [Physical Review B 84 224403 (2011); Advanced Functional Materials 22, 989 (2012)]. To date, no spin injector device can be described as satisfactory. One of the objectives of the present application is to arrive at another device, preferably checking one or more of the above-mentioned criteria. PRESENTATION OF THE INVENTION The present application relates to a device for injecting polarized spins into an organic layer, also called a polarized spin injector, on a spins polarized current source and a multipurpose device as defined below. These devices verify one or more of the above criteria, in order to be exploitable in the field of electronics or microelectronics. A spin-polarized current source designates a device for polarizing, in the same direction and in the same direction, the spin moments of a majority of electrons passing through the device. A source of polarized current in spins thus comprises a current source, connected to a polarized spin injector device, for filtering the electrons from the current source according to their spin. A polarized spins injector device according to the invention comprises: an electrically conductive material, called a substrate, a first surface of which has magnetic properties; an organic layer comprising a first face facing a second, the first face comprising at least partly a set of atoms substantially in the same plane, and linked between them by parallel atomic bonds or substantially parallel to the first face of the substrate. The atoms of the first face of the organic layer may have, either alone or by combination (e.g., one or more dimers), a paramagnetic state. In contact with the first face of the substrate, the atoms of the organic layer then form an interface, called filtering interface. The paramagnetic state of at least a portion of the organic layer atoms can also be induced by charge transfer at the substrate / organic layer interface. The spin injector device (biased) filters 75% or more of 75%, preferably more than 85%, of conduction electrons from the substrate and passing through the filter interface; according to their state of spin polarization, relative to the spin repository printed by the magnetism of the substrate; when its temperature is greater than -220 ° C, or -20 ° C, or 0 ° C or 150 ° C or 200 ° C. The first face of the organic layer may be chemically adsorbed by the first face of the substrate, i.e., chemical bonds may be established between the atomic species composing the first face of the substrate and the first face of the substrate. organic layer. Advantageously, the chemical adsorption phenomenon may allow the organic layer to form a conductive extension of the substrate, which is normally restricted to only the atoms of said substrate. The spin polarization on the organic sites will not be acquired at the cost of increasing the resistance of the device as may be the case for Fe / MgO type tunnel junctions.

In order to promote interactions between said first faces, their molecular planes in contact can be complete. The chemical bonds between the first face of the substrate and the first face of the organic layer are preferably characterized by magnetic molecular orbitals. In other words, the magnetism (diamagnetism and / or paramagnetism) of the first face of the organic layer couples with the magnetism (ferrimagnetism, and / or ferromagnetism, and / or antiferromagnetism) of the first face of the substrate. This coupling phenomenon is preferentially due to the overlap of the orbital bonds between the atoms composing said first faces.

At least two adjacent atoms at the first organic face may share a pi-type linkage parallel or substantially parallel to the filter interface. In other words, the orbital lobes of two adjacent atoms of the first face of the organic layer, forming a covalent bond, are parallel to each other, and perpendicular or substantially perpendicular to the first face of the substrate. The spatial extension of the density of states resulting from the pi bond (that is to say the electron cloud resulting from the link) is, for its part, preferably parallel or substantially parallel to the first face of the substrate. This pi bond forms a paramagnetic state that can advantageously interact with the magnetic substrate. This interaction is advantageously increased because of the spatial shift of this electronic cloud, a shift inherent in the nature of this pi bond parallel to the face of the substrate, towards the atoms of the face of the substrate. The first face of the substrate preferably has a magnetic order characterized by a long range order of the magnetic moments of the atoms (or a subset of atoms). A long-range order is defined by a distance greater than the distances separating the first, second, or third neighboring atoms surrounding an atom present at said first face. The first face of the substrate may be at least partially or completely antiferromagnetic and be characterized by a Néel temperature, TN, greater than the temperature of the liquid nitrogen, for example greater than -220 ° C, or greater than -20 ° C, or 0 ° C or 150 ° C or 300 ° C. This antiferromagnetic order can then be carried by atomic subarrays of different species, each sub-network of species being able to be ordered ferromagnetically, so that the filtering properties of the filtering interface are carried by at least one of these subnets. Preferably, the Néel temperature of the substrate is higher than the operating temperatures of electronic devices. The first face of the substrate may be at least partially or wholly ferromagnetic and be characterized by a Curie temperature, Tc, within the same ranges of values as the Néel temperatures cited above. The first face of the substrate may be at least partially or entirely ferrimagnetic so that one of the spin subarrays, carried by a sub-network of atomic sites composing the ferrimagnetic material, has ferromagnetic properties similar to those stated in the preceding paragraph, so that the filtering properties of the filtering interface are carried by one of these sub-networks.

The first face of the substrate may comprise one or more antiferromagnetic and / or ferromagnetic and / or ferrimagnetic preceding zones. Néel's temperature, like the Curie temperature, refers to the temperature above which a magnetic material becomes paramagnetic. Above this temperature, the thermal energy is sufficient to break the magnetic order of the first face of the substrate.

The first face of the substrate may be composed of one or more metals or metal alloys, composed of the following elements: cobalt, and / or nickel, and / or iron, and / or an alloy of iron or cobalt with metals of the type 4d or / and 5d such as palladium and / or platinum, and / or one or more magnetic oxides such as Fe304 or TiO (2 '). The organic layer covering the first face of the substrate may be composed of electrically insulating or semiconductor elements, nitrogen or carbon type or carbon dimers and / or oxygen or by phenanthroline. The magnetic properties of the first face of the substrate are possibly addressable via a magnetic field or an external current. The first face and the second face of the organic layer may be parallel or substantially parallel to each other and / or separated by a distance equal to a molecular plane or lnm. A spin polarized current source can be obtained from a previous device, when: an electrically conductive material, called a mass, is located above and opposite the organic layer; the first face of the substrate and the face of the mass closest to the preceding one, called the first face of the mass, are electrically connected to a current source, so as to allow a flow of conduction electrons to pass through the filter interface. Preferably, the first face of the mass is spaced a sufficient distance from the substrate, so as not to disturb the atomic bonds forming between the substrate and the organic layer at the filter interface. In other words, the first face of the mass is separated from the filtering interface to limit or avoid the overlap of the wave functions describing the atomic bonds, between the atoms constituting the first face of the substrate, and the wave functions describing the atomic bonds between the atoms constituting the first face of the mass.

Two wave functions overlap when a portion of the spatial extension of each occupies the same space. The electrical intensity applied between the first face of the substrate and the first face of the mass, is preferably less than the breakdown intensity or the disruptive intensity, between said first faces. The second face of the organic layer and the first face of the mass may be separated by a distance greater than or equal to 1 nm. The space between the second face of the organic layer and the first face of the mass may be filled by a fluid, for example air or a neutral gas. This space can also be filled by an electrically insulating or semiconductor material, preferably of organic type, such as tris (8-hydroxyquinoline) aluminum (III) (Alq 3), porphyrin, phthalocyanine (Pc), 5, 6, 11 , 12-tetraphenylnaphthacene (rubrene), perylene-3,4,9,10-tetracarboxylic dianhydride (PCTDA), tetracyanoethylene (TCNE), tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ), Fe-phenanthroline. Optionally, this material may be identical in nature to the organic layer. The present application also relates to a so-called multi-purpose device, comprising two prior polarized spin injector devices, their organic layers being held together via a layer, called intermediate layer. The first spin injector device 10 makes it possible to spin polarize a stream of electrons coming from the substrate of this device and passing through its filtering interface. The second spin injector device makes it possible to measure or read the polarization state of this flux. The intermediate layer is preferably of organic nature and has a thickness: less than 3 nm in order to promote an elastic tunneling transport of the electrons between the two devices, preferably by avoiding disturbing or degrading the properties of the two filtering interfaces of the two. devices - equal to or greater than 3 nm to promote hopping or diffusive effect. The roles of the two spin injector devices, respectively that for polarizing the spins (or writing), and that for reading the state of polarization of the spins of the current, depend on the direction of the current flowing through them. Thus, these roles can be reversed by changing the propagation direction of the current in the multipurpose device.

Thus, if the current emanates from the substrate of the second device, then the first device will read the polarization in spins of the current emanating from the second device.

The second device may be replaced by any electrical element whose spin polarization of the current passing through it is to be measured by means of a first spin injector device, as long as this electric element does not disturb the spin filtering function of the filtering interface of the first spin injector device. The invention also relates to a method for producing a polarized spin injector device as described above, comprising the following steps: depositing on a first face a substrate having magnetic properties, and preferably flat surface, an organic layer; positioning the mass facing the organic layer at a distance sufficient to avoid modifying the magnetic properties of the substrate and of the organic layer; electrically connecting the first face of the substrate and the first face of the mass, respectively to a first electrode and a second electrode of the same intensity source; aligning the magnetization of the substrate in order to obtain the direction and the direction of spin of the desired current. The present application also relates to a method of using a preceding polyvalent device, comprising the following steps: depositing on a first face a substrate having magnetic properties, and preferably of flat surface, of a layer organic ; deposition of the intermediate organic layer; depositing on the second face of the organic layer a second ferromagnetic layer; electrically connecting the first face of the substrate and the second face of the second ferromagnetic layer, respectively to a first electrode and a second electrode of the same intensity source; aligning the magnetization orientations of the substrate and the second ferromagnetic layer in such a way as to be able to carry out the parallel parallel and antiparallel alignments of the two layers; measuring the resistance and / or conductance and / or impedance of the polyvalent device according to said parallel and antiparallel alignment alignment configurations of the magnetization of the substrate and of the second ferromagnetic layer. This makes it possible to determine the spin polarization of the current flowing through the multipurpose device. Eventually reverse the direction of the current in order to invert the write and read roles of the two interfaces of the multipurpose device. A spin-polarized current source can be used in at least one step of applying an electrical intensity via the current source between the first face of the substrate and the first face of the mass of the spin injector device. when it is at a temperature greater than -220 ° C, or greater than -20 ° C, or 0 ° C or 150 ° C or 200 ° C or 700 ° C. When an electrical intensity is applied between the first face of the substrate and the first face of the mass, more than 75%, preferably more than 85%, of the electrons passing through the filtering interface have their spin polarized in the same direction and the same direction corresponding to the direction of magnetization of the substrate. This polarization can be either positive (spin-up electrons) or negative (spin-down electrons). In other words, a spin-polarized current source can be used or operated in environments in which electronic devices operate. The electrical intensity applied between the first face of the substrate and the first face of the mass may vary as a function of the distance separating said first two faces, and elements arranged between said faces, so that the intensity is less than breakdown intensity between said faces. BRIEF DESCRIPTION OF THE DRAWINGS Other details and features of the invention will become apparent from the description which follows, with reference to the following appended figures. Identical, similar or equivalent parts of the different figures bear the same references in order to facilitate the passage from one figure to another.

The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable. FIG. 1 represents a polarized spin injection device 1. FIG. 2 represents a spin polarized current source 2. FIG. 3 represents a polyvalent device 4.

FIG. 4 represents measurements carried out, at a temperature of 25 ° C., by spin-polarized photoemission, close to the Fermi level, at the interface between an organic layer and a magnetic layer, present at the devices 1 and 2 and 3. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Now, several examples of polarized spin injector devices, spin polarized intensity sources, multipurpose devices, as well as their method of production and use will be described. . One of the objectives of the invention is to propose a source of spin-polarized current, making it possible to polarize in the same direction and in the same direction, more than 75%, preferably more than 85%, of the electrons passing through the device. . The operating temperature of the device is preferably within the range of operating temperatures of the microelectronic devices. These are generally between -20 ° C and 150 ° C. More broadly, the operating temperatures of a spin-polarized current source may be at non-zero temperature, and in particular for applicative reasons greater than the temperature of liquid nitrogen, ie about -200 ° C., or well above 200 ° C for applications in extreme environments. In other words, the present application wishes to propose a new source of spin polarized current, comprising a polarized spin injector device, and exploitable at the industrial level. A polarized spins injector device 1 comprises a first electrically conductive material, called substrate 10, a first face 11 of which is in contact with the external environment and has magnetic properties of ferromagnetic and / or ferrimagnetic and / or antiferromagnetic type (FIG. 1). The first face 11 of the substrate may for example be based on oxide (s), and / or nitrite (s), and / or carbide (s), or based on cobalt, and / or iron, and / or nickel and / or iron or cobalt alloy with 4d or 5d type materials (for example such as FePt and / or CoPd). The first face of the substrate 10 is preferably crystallized, according to a structure promoting spin polarized states at its surface, for a range of energy between -LEV <E-EF <+ leV, and likely to couple electronically to the states of the organic layer 20 described below.

When the first face of the substrate comprises cobalt, the latter may have a crystalline structure of the face-centered cubic type (cfc), the orientation of the crystallographic planes being defined by the following Miller indices (001). The first face 11 is covered, at least in part, by a layer of organic material 20. The layer of organic material is delimited by a first face 21 and a second face 22 vis-à-vis. The minimum distance between the faces 21 and 22 of the organic layer corresponds to the spatial extension of the molecule forming the layer, in a direction perpendicular to the surface 21 of the organic layer. This distance can reach twice this spatial extension. The first face 21 is in contact with the first face 11 of the substrate 10, so as to form an interface called filter interface. The first faces are adsorbed at this interface. Preferably, the first face 11 of the substrate is planar so as to promote or optimize this adsorption phenomenon between the two faces 11 and 21. Advantageously, in order to promote the preceding interactions between said first faces, the organic molecule forming the first face 21 is flat or substantially flat, to promote its polarization by the first face 11 of the substrate. For the same reason, the molecular plane of the first face is preferably complete.

The atomic bonds between the atoms making up the first face 21 of the organic layer are preferably parallel or substantially parallel to the first face 11 of the substrate.

The organic layer may be composed of carbon atoms, and / or nitrogen, and / or oxygen, and / or boron, and / or hydrogen. An organic layer 20 may for example be a layer of the family of porphyrins such as phthalocyanine (Pc = C32F118N8).

This layer may optionally be doped with metal elements such as manganese (Mn). From one of the preceding spin injector devices 1, a spin polarized source 2 can be obtained (FIG. 2). For this purpose, a second electrically conductive material 30, called a mass, is opposite the first face 11 of the substrate, the organic layer 20 being situated between the mass and the substrate. The mass 30 is preferably at a sufficiently distant distance from said first face 11, so as not to modify or influence the magnetic properties of the filter interface. In other words, the mass is sufficiently spaced from the first face 11 of the substrate, so as not to disturb or prevent the coupling of the atomic bonds between said first face 11 and the atomic plane of the organic layer 20 in contact with the substrate 10. For example, the distance separating the first face 31 of the mass 30, the closest face and vis-à-vis the first face 11 of the substrate, may be equal to or greater than 1 nm, or 3 nm, or 10 nm, or 100 nm or 1000nm. Preferably, the first face 31 is of flat surface and parallel to the first face of the substrate. The substrate 10 and the ground 30 are respectively connected to the electrodes 41 and 42 of a current source 40, so that, when the power source is turned on, an electric current or a conduction electron flow passes through the device, perpendicularly or substantially perpendicular to the filter interface (Figure 2). The present application also relates to a device comprising two spin injector devices 1 and 1 'as described above. These devices are placed vis-à-vis, more precisely, their organic layers (20, 20 ') are face-to-face and separated by an intermediate layer 50 (Figure 2). Such a device is called versatile device 3 in the present application because, it allows both: - spin polarize a stream of electrons passing through the first spin injector device 1; and to measure or read the state of polarization of this flux via the second spin injector device 1 '. The intermediate layer 50 advantageously makes it possible to transmit a stream of electrons between the two devices 1 and 1 ', preferably by influencing as little as possible the state of polarization of the electrons composing said stream. It may be of organic nature and have a thickness defined in a direction perpendicular to one of the filtering interfaces: A) less than 3 nm, in order to promote elastic tunneling of the electrons between the two devices 1 and 1 '; - B) equal to or greater than 3nm, to promote a transport by "hopping" or by diffusive effect between said devices. In case A), the transport will be generally insensitive to the structural defects of the organic layer. In case B), the transport will be carried out over greater distances that are conducive to the transport of the information encoded by the spin of the electrons forming the electric current.

The intermediate layer 50 may be composed of the aforementioned materials relating to the organic layer 20, as well as carbon nanotubes and graphene. Thanks to the low band dispersion of the interface state allowing the spin filtering, the electric transport which is carried out perpendicularly or substantially perpendicularly through the filtering interface can then adopt a different propagation direction during the transport to the through the material constituting the intermediate layer 50, for example carbon nanotubes or graphene. In order to read the state of spin polarization of the electron flux, the substrate 10 can be connected to a first terminal 41 of a current source 40; and the substrate 10 'at a second terminal 42 of the same current source 40. It is then possible to measure the resistance (or conductance, or impedance) of the multipurpose device 3 after establishing a parallel / antiparallel orientation of the magnetization of the two layers. 10 and 10 '. If the current whose spin polarization is to be measured does not have a reference frame (that is to say a direction and a direction) established, then the resistance of the polyvalent device 3 will be measured while varying in three dimensions. orientation of the magnetization of the ferromagnetic layer 10 'serving as reading layer.

The invention also relates to a process for producing a spin injector device above, comprising at least one step of depositing or forming an organic layer of phthalocyanine (Pc) on a cobalt substrate 10. The face 11 of the substrate can be crystallized, the crystallization planes defining a face-centered cubic structure (cfc) whose orientation is defined by the following Miller indices: (001). The deposition of the organic phthalocyanine layer can be carried out in a vacuum chamber, in which the pressure is less than 3x10-8 mbar. The organic layer may be deposited by a so-called "needle-valve" sublimation technique, for which the vapor phase molecules are introduced at the face 11 of the substrate 10 by means of a nozzle (Review Scientific Instruments, 82). , 033903 (2011); http://dx.doi.org/10.1063/1.3553010). The foregoing method can be completed by the following steps to obtain a spin-polarized current source 2: - positioning a mass 30 above and opposite the organic layer 20 at a fixed distance ; connecting the substrate 10 to a first terminal 41 of a current source 40; - Connection of the mass 30 to a second terminal 42 of the same current source 40. It is also possible to obtain a versatile device 3 as described above, from two spin injector devices, according to the following steps: assembling two preceding spin injector devices 1 and 1 ', via an organic layer 50 placed between said devices; Connecting the substrate 10 to a first terminal 41 of a current source 40; connecting the mass 30 to a second terminal 42 of the same current source 40; aligning the magnetization orientations of the two devices in such a way as to be able to carry out the parallel parallel and antiparallel alignments; measuring the resistance of the multipurpose device according to said magnetization orientations, in order to measure or read the degree of polarization of the current [A. Fert, Nobel ACS Readings 2008]. We will now describe a method of using a spin 2 polarized current source having a 0.3nm thick H2Pc layer deposited on a crystallized cobalt substrate (CFC, (001)). The polarized current source may be operated in an environment having a temperature greater than -20 ° C, or 0 ° C, or 50 ° C, or 100 ° C, or 200 ° C. For this, the current source 40 which is connected to the substrate 10 and the ground 30, is turned on (Figure 2). The applied voltage is chosen so that it is below the voltage threshold capable of producing an electric arc between the substrate and the ground, in other words, an electrical breakdown. This voltage threshold depends on the distance separating these two elements, as well as the electrical properties of the element or elements present between the substrate and the mass. The conduction electrons, produced by the current source 40 and passing through the substrate / organic layer interface, are then filtered according to the orientation of their spin. More than 75%, preferably more than 85%, of electrons passing through said interface or filter interface have their spin polarized in the same direction and direction. This remarkable result was confirmed by spin-polarized photoemission measurements made from a measuring device called a Mott detector, coupled to an intense light source in the range of soft and ultraviolet X-rays, from a synchrotron light source [Solid State Communications 37, 771 (1981) http://dx.doi.org/10.1016/0038-1098(81)91171-6http: //www.sciencedirect.com/science? ob = RedirectURL & 30 method = outwardLink & partnerName = 936 & eid = 1-s2.0-0038109881911716 & pii = 0038109881911716 & origin = article & area = art page & targetURL = https% 3A% 2F% 2Fs100.copyright. com% 2FAppDispatchServlet% 3FpublisherName% 3DELS% 26content tID% 3D0038109881911716% 26orderBeanReset% 3Dtrue & acct = C0 00008898 & version = l & userid = 113008 & md5 = f0815afbldfbf964 dbf2e63cf243c6b3]. The synchrotron light source has a strong luminous flux allowing to detect small quantities of matter and especially to adjust at will the energy of the photons, which makes it possible to vary the effective section, in other words the sensitivity of the detection compared to to the different elements present in the device. The energies chosen must remain low (<100eV) in order to highlight the characteristic spin-polarized structures with low binding energy. By choosing a photon energy of 20eV, the detection of light atoms (carbon, nitrogen) with respect to cobalt is favored. At 40 eV, heavier elements, magnetic metals, are favored in detection.

This sample-directed energy source includes the filter interface, which is at the boundary between the organic layer 20 and the cobalt layer 10 (Figure 1). The measurements are carried out at room temperature, ie at about 25 ° C.

A Mott-type detector makes it possible to measure the spin polarization of the photoelectrons emitted by said filtering interface. This detector has an effective Sherman factor of 0.15 (a factor determining the spin sensitivity of this type of detector). This limitation reflects the physical process of measurement (the spin-orbit interaction induces an asymmetry in the probability of back scattering of high energy spin polarized electrons on heavy atoms, this diffusion process is called "Mott scattering").

The intensity of photoemission for each spin channel is then measured on a set of substrate 10 and organic layer 20 as a function of their binding energy, that is to say relative to the Fermi level of the interface 21. This intensity is separately measured for each spin channel and binding energy for the single substrate 10. By spin channel subtraction of the intensity from only the substrate 10 relative to that of the substrate assembly 10 and organic layer 20 subtraction which takes into account the attenuation of the photoelectrons from the substrate 10 through the organic layer 20, we can then obtain the dependence on the binding energy of the photoemission intensity of the only interface 21, which is composed electrons forming the chemical bonds between the first face 11 of the substrate 10 and the first face 21 of the organic layer 20 This dependence is presented in FIG. it is surprising that more than 80% of the electrons bound to the atoms, present at the level of the filtering interface, of energy close to or equal to the Fermi level (which corresponds to the value 0 at the level of the abscissae of the graphs present in FIG. 4), have the same spin polarization state.

Only spin polarized electrons of the up type, for a relative energy equal to zero (AA '), are detected (FIG. 4). Conversely, for the same relative energy, the down-type polarized electrons, symbolized by solid triangles, are not detected. Their signal becomes measurable for 20eV energy probe photons only from a relative energy lower than E-EF - = + 0.13eV (BB ') (Figure 4). This detection threshold decreases for photons of 40eV when the weight of Co in the spectrum becomes more dominant. Given systematic errors related to the detection apparatus, we estimate that the result reflects a spin polarization close to / at the Fermi level of more than 80%. However, the electrical conductivity of a material directly depends on the number of electrons present at the level of the Fermi energy. As a result, the conduction electrons, passing through the filtering interface, will perceive a different conductivity depending on whether their spin polarization is identical or not to the state of polarization of the largest electron population at the level of the the Fermi energy. In other words, the conduction electrons can propagate through the filtering interface in two different resistivity channels. The resistivity is inversely proportional to the number of electrons having the same state of spin polarization at the Fermi energy level. The difference in resistivity between these two channels depends on the quality of spin filtering of the conduction electrons. The present measurements show that a spin injector device formed by a H2Pc layer on a crystallized cobalt layer, makes it possible to obtain a filtering interface comprising more than 80% of the Fermi electrons having the same state of polarization. (Figure 4). This interface therefore forms a polarized spindle injector exploitable industrially.

In other words, an industrially exploitable polarized spin injector can thus be formed from an organic layer in contact with a layer having magnetic properties. For this, it is preferable that: a) the atoms constituting the layer with magnetic properties 10, which is in contact with the organic layer 20, have their electrons at Fermi level or in the range -leV <E-EF <+ leV polarized and magnetically ordered; b) the atoms of the organic layer have a paramagnetic order, which can be obtained by means of pi bonds between them, or by all connections allowing a spatial overlap and of the same energy of these orbitals with those of the atoms of the surface of the substrate 10. By hybridization of the molecule following its adsorption on the surface of the substrate 10, the paramagnetic state of the atoms of the molecule constituting the organic layer is then magnetically ordered; Up to now, comparable filtering values (of the order of 80%) have only been observed with organic devices operating in temperature ranges below -220 ° C. Such devices are therefore not exploitable in the field of microelectronics.

To date, it has been accepted by the scientific community that the filtering rate, for a polarized jet injector device comprising an interface between ferromagnetic materials and organic materials, can come from the presence of structural defects at the interface (Nature Phys. , 615 (2010)). However, this filtering mechanism degrades with temperature. As a result, it is considered impossible to obtain filter rates higher than 80% for such devices operating at temperatures above -220 ° C. Recent modeling work has shown that the first atomic layer of a manganese ion-doped Pc layer deposited on a cobalt substrate has a state density to polarize only 25% of the electrons crossing the interface. filtering (Physical Review Letters, 105, 077201 (2010)). This work also suggests that modification of the central site may alter spin polarization. These calculations were made considering that the device operates at the theoretical absolute zero temperature, about -273.15 ° C! Because of these unrealizable conditions, these results are obviously not transposable for real devices. In other words, these studies do not call into question hypotheses and observations showing a deterioration in the quality of polarized spin filtering when the temperature of the device increases (Nature Phys., 6, 615 (2010), Nature Physics 6, 562 ( 2010)).

In addition, it has been observed from devices, this time real, having an interface between ferromagnetic materials and organic materials, that the performance of the ferromagnetic materials depends directly on the chemical order of the atoms that make up the alloy. This order is very difficult to obtain experimentally, it is all the more so at the industrial level. The theoretical model above does not take into account this difficulty of realization. Moreover, this same theoretical model is not viable for describing the spin filtering properties of this type of interface because it does not take into account the inter-diffusion phenomena occurring between the layers at their time. elaboration, a phenomenon known to be destructive of the spintronic properties of an interface. Other experimental and theoretical results also suggest that the central site of the Pc molecule can influence spin polarization at the interface with a ferromagnetic material [Physical Review B 84 224403 (2011); Advanced Functional Materials 22, 989 (2012)]. However, these studies do not suggest that it is possible, by means of such interfaces, to obtain a spin polarization sufficiently strong to be used industrially in a competitive manner. Moreover, in [Advanced Functional Materials 22, 989 (2012)], the authors suggest that moving from a perpendicular bond (FePc, CoPc) to a planar bond (CuPc) emanating from the Co substrate could (taking into account the poor signal-to-noise ratio of the experimental results) increase the spin polarization (from almost 0% to -30%) without however making it competitive industrially. Finally, the interface between Fe cc (001) and CuPc would replicate, without the appearance of interface states, the spin polarization (-40%) of the underlying Fe [Physical Review B 84 224403 (2011)]. The inventors believe that the relative banality of these results reflects both the sensitivity of the experimental techniques used and the quality / inventiveness of the analysis of the results obtained. Surprisingly, and contrary to what was hitherto admitted by the scientific community, the inventors were the first to obtain an industrially exploitable spin injector device, in particular of very strong spin polarization (greater than 80%). , by depositing a layer of H2Pc on a layer of cobalt. Specifically, an organic layer of H2Pc was deposited on a ferromagnetic Co layer, covering a crystallized Cu (001) substrate. More precisely still, the experiment was repeated with the same results for other substantially two-dimensional molecules (MnPc, pi-bonded carbon atoms), as well as three-dimensional Fe-phenanthroline molecules of which a subset of atoms exhibit parallel or substantially parallel connections to the surface 11 of the substrate. The above results show that the filtering properties of this type of interface are: intrinsic to the device; - essentially independent of the central site within the phthalocyanine cage; - Dependent on the polarization of perpendicular or substantially perpendicular electronic orbitals which bond the atoms of the organic layer to the atoms composing the magnetic layer. It follows from this that it is preferable that the linear combinations of molecular orbital adsorption of the organic layer, on the magnetic substrate, be those of a paramagnetic state which will more easily couple to the magnetism of the substrate. For this, the magnetic layer preferably comprises at least one ferromagnetic and / or antiferromagnetic and / or ferrimagnetic zone, in contact with the organic layer. In other words, two atoms of the first face 21 of the organic layer 20, sharing a pi bond and adsorbed on the substrate 10, will have their density of state at the Fermi level, and will be strongly polarized in spin as long as the magnetic properties of the first face of the substrate are preserved. The spin filtering properties of such a device will be constant as long as the thermal energy is insufficient to break the magnetic order of the first face of the substrate. As a result, the filtering properties of a spin injector device as described above can be maintained at temperatures above -220 ° C, or -20 ° C or 0 ° C, or 150 ° C, or 200 ° C, as long as the first face 11 of the substrate 10 retains its magnetic properties in the preceding temperature range. The first face 11 of the substrate is thus chosen so that its Néel or Curie temperature is greater or much greater than the operating temperatures of the device. For example, a cobalt layer of at least 3 monolayers (ie about 0.5 nm thick) sandwiched between a copper substrate and a previous organic layer, forms a filtering interface (> 75%) operating up to temperatures of the order of 230 ° C. This interface can thus polarize the current coming from the cobalt layer, or even allow the detection of the spin polarization of a current in the direction of the cobalt layer.

In the context of a versatile device, this interface can read the amplitude of the polarized current from an electrical device affixed to it, and towards the cobalt layer, since this device does not degrade the properties filtering the interface (see considerations above). According to another implementation, a polyvalent device can consist of a stack, made on Si (001), of Cu (70nm) / Ni (5nm), then of a ferromagnetic layer 10 of cobalt cfc (001) from less 0.5nm [Phys. Rev. B 60 4087 (1999)], on which the organic interface layer H2Pc of 0.3nm is deposited, then the organic layer H2Pc intermediate of 2.4nm, then the interface layer 20 'of H2Pc of 0.3nm, then the ferromagnetic layer 10 'of cobalt of 100 nm, optionally magnetically hardened with 2.5 nm CoO and optionally protected with a gold layer. The quality of the upper filter interface can be improved by cold cobalt deposition (T = -220C). The spin filtering at the two interfaces generates a relative difference in resistance of the multipurpose device for the two parallel and antiparallel orientations of relative magnetization of the ferromagnetic layers exceeding 300% (for a spin polarization of each of the two interfaces of more than 80% and without further spin filtration due to transmission through the organic barrier), up to temperatures of the order of 230 ° C., the temperature limited here by the structural stability of the metal stack before the ferromagnetic substrate 10 In conclusion, the present application makes it possible to manufacture and use a polarized jet injector device, as well as a spin-polarized current source device that is industrially exploitable because it complies with at least one of the following criteria: Filtering interface of the device makes it possible to select or filter more than 75%, preferably more than 85%, of the conductive electrons crossing it; 2) this filtering rate in polarized spins can be maintained as long as the Curie or Néel temperature of the first face of the substrate is greater than the operating temperatures of the device; 3) the magnetic materials as well as the organic materials used to form the device are abundant or easily synthesizable and easy to assemble according to the techniques commonly used in the electronics industry; 4) these manufacturing techniques also make it possible to form devices that are not very resistive, especially when they are produced at nanometric dimensions, since the organic layer adsorbed on the metal substrate itself becomes metallic; therefore, the spin injector device, such as the spin polarized current source, can be electrically related to an ohmic conductor; 5) the spin injector device, such as the spin-polarized current source, enables conduction electrons to be injected over long distances in organic materials without modifying their spin polarization state; these two devices, by their use of an organic layer, are particularly suitable for the injection of polarized spins into organic semiconductors.

Claims (15)

REVENDICATIONS1. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron flow, passing through the device at a temperature above -220 ° C, depending on the state of polarization of said electrons comprising: - an electrically conductive material, referred to as a substrate (10), having a first face (11) with magnetic properties; an organic layer (20) having a first face (21) opposite a second face (22), the first face (21) comprising at least partly a set of atoms substantially in a same plane, and linked together by atomic links parallel or substantially parallel to the first face (11) of the substrate (10), and in contact with the first face (11) so as to form an interface, said filtering interface. 20 2. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron stream according to claim 1, the first face (21) of the organic layer (20) being chemically adsorbed by the first face (11) of the substrate (10). 3. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron stream according to claim 1, the chemical bonds between the first face (11) of the substrate (10) and the first face (21) of the organic layer (20) being characterized by paramagnetic molecular orbitals. 4. Device for filtering 75% or more than 75%, preferably more than 85%, of an electron flow according to one of claims 2 or 3, two adjacent atoms at the level of the first organic surface sharing a pi-type link, an electron cloud parallel or substantially parallel to the filtering interface, and promoting a paramagnetic state. 5. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron stream according to one of claims 1 to 4, the first face (11) of the substrate (10) being at least partially antiferromagnetic, characterized by a Néel temperature greater than -220 ° C. 20 6. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron flow according to one of claims 1 to 5, the first face (11) of the substrate (10) being at least partially ferromagnetic or ferrimagnetic, characterized by a Curie temperature greater than -220 ° C. 7. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron flux according to one of claims 1 to 6, the face (11) of the substrate (10) being composed of at least one of: cobalt, and / or nickel, and / or iron, and / or an alloy of iron or cobalt with 4d and / or 5d metals such as palladium and / or platinum, and / or one or more magnetic oxides such as Fe304 or Ti0 (2,). 8. Device for filtering 75% or more of 75%, preferably more than 85%, of an electron flow according to one of claims 1 to 7, the organic layer (20) being composed of electrically insulators or semiconductors, of carbon type or dimers of carbon and / or oxygen, or by phenanthroline. 9. Spin-polarized current source comprising a device according to one of claims 1 to 8, comprising: an electrically conductive material, called mass (30), situated above and opposite the organic layer (20); a source of current (40) electrically connected to the first face (11) of the substrate (10) and to the face (31) of the mass (30) closest to the previous face, so as to allow a flow of conduction electrons to cross the filter interface. 10. Spin-polarized current source according to claim 9, the first face (31) of the mass (30) being spaced a sufficient distance from the substrate (10), so as not to disturb the atomic bonds forming between the substrate ( 10) and the organic layer (20) at the filter interface. A spin polarized current source according to claim 9 or 10, the space between the second face (21) of the organic layer (20) and the first face (31) of the mass (30) being filled with a material following organic: Alq3, Pc, rubrene, PCTDA, TCNE, TTF, TCNQ, Fe-phenanthroline. 12. Versatile device comprising two devices defined according to one of claims 1 to 8, characterized in that their organic layers (20, 20 ') are held together by means of a layer, called intermediate layer. 13. A method of using a spin-polarized current source according to one of claims 9 to 11, wherein an electric intensity is applied between the first face (11) of the substrate (10) and the first face (31). of the mass (30) when the spin-polarized source is in an environment having a temperature greater than -220 ° C. 14. A method of using a spin polarized current source according to claim 13, the electrical voltage applied between the first face (11) of the substrate and the first face (31) of the mass less than the breakdown voltage. between these two elements. 15. A method of using a spin polarized current source according to claim 13 or 14, 75% or more of 75%, preferably more than 85%, of electrons traversing perpendicular or substantially perpendicular to the interface. substrate / organic layer being polarized in a same direction determined by the orientation of the magnetization of the substrate (10).